Variable resistor of lead screw actuated-type with contact engaging screw threads

ABSTRACT

A variable resistor comprises a rotatable screw shaft having a screw on the outer periphery thereof, a resistor disposed in parallel with the screw shaft, a movable member formed of a bent leaf spring of electroconductive metal, and a movable member holder through which the screw shaft passes. The movable member holder holds the movable member. The movable member has at one end thereof a slidable contact portion contacting with the resistor. The other end of the movable member contacts with the portions of the grooves of the screw having the effective screw diameter. The movable member also has a protuberant middle portion contacting with adjacent crests of the screw. The edge line of the other end of the movable member has an inclination angle with respect to a vertical plane to the axis of the screw shaft, which angle is reverse in direction to the lead angle of the screw and substantially equal to the lead angle in absolute value.

United States Patent Takashi Yamamura lwai-Machi, Sashima-gun, Japan45,777

June 12, 1970 Dec. 28, 1971 Victor Company of Japan Ltd. Yokohama,Kanagawa-ken, Japan June 12, 1969 Japan Inventor Appl. No. FiledPatented Assignee Priority VARIABLE RESISTOR 0F LEAD SCREW ACTUATED TYPEWITH CONTACT ENGAGING SCREW THREADS 2 Claims, 8 Drawing Figs.

US. Cl 338/202, 3 38/ l 80 Int. Cl H0lc 9/02 Field of Search 338/ 160,

References Cited UNITED STATES PATENTS 8/1968 Soulakis 338/180 3,124,7803/1964 Hulbert 338/180 X FOREIGN PATENTS 722,284 1/1955 Great Britain338/l 80 Primary Examiner- Lewis H. Myers Assistant Examiner-Gerald P.Tolin Attorney-Waters, Roditi, Schwartz and Nissen ABSTRACT: A variableresistor comprises a rotatable screw shaft having a screw on the outerperiphery thereof, a resistor disposed in parallel with the screw shaft,a movable member formed of a bent leaf spring of electroconductivemetal, and a movable member holder through which the screw shaft passes.The movable member holder holds the movable member. The movable memberhas at one end thereof a slidable contact portion contacting with theresistor. The other end of the movable member contacts with the portionsof the grooves of the screw having the effective screw diameter Themovable member also has a protuberant middle portion contacting withadjacent crests of the screw. The edge line of the other end of themovable member has an inclination angle with respect to a vertical planeto the axis of the screw shaft, which angle is reverse in direction tothe lead angle of the screw and substantially equal to the lead angle inabsolute value.

PATENTED DEB28 I97! SHEET 1 [IF 2 FIG. 2

FIG.

-21/7 ,Tlo

mimiuumzam 363L372 SHEET 2 [IF 2 VARIABLE RESISTOR OF LEAD SCREWACTUATED- TYPE WITH CONTACT ENGAGING SCREW THREADS This inventionrelates to a variable resistor, and more particularly to a structure ofa variable resistor of lead screw actuated type used for a noncontactsystem tuner in a television receiver.

In the television receiver which receives the television broadcastingsignals in VI-IF and UHF frequency ranges, generally a noncontact-typeelectronic tuner has been proposed as a tuner for switching respectivechannels of VHF and UHF. A conventional VHF tuner has employed a systemof switching the circuit of each channel by means of contacts, while aconventional UHF tuner has adopted a system for tuning each channel bymeans of a variable capacitor. In contrast with these tuners thenoncontact-type electronic tuner employs a variable capacitance elementas a tuning element, which varies its capacitance by applied voltage. ADC voltage applied in the variable capacitance element should beappropriately changed so as to select the low channels of VHF, highchannels of VHF, and channels of UHF. Therefore, in the appropriateadjusting of the DC voltage, the tuner needs a variable resistor ofextremely small and simple construction operating accurately.

A variable resistor of lead screw actuated type which is used in theconventional noncontact-type electronic tuner usually has a movablemember which has at an end a contact portion to slidably contact theresistor and at the other end a bent portion engaging with spiral screwgrooves of a rotating screw shaft. In this mechanism, the movable memberengages with the bottom of the screw thread or the root at the only bentportion. The conventional variable resistor of the described type hasyet the following disadvantages. In the event that the pressure of thecontact is intensified, the engagement of the bent portion is worsenedthereby producing racings or idle rotations of the screw shaft.Inversely when the contact pressure is weakened for obtaining a goodengagement of the bent portion it causes a bad contact with theresistor. The weak contact also causes undesired displacements of thesliding position of the movable member by small shocks. Moreover thereis an increased backlash member between the bent portion and the screwgroove of the screw shaft. Therefore the accurate movement of themovable member is made impossible relative to the rotation of the screwshaft.

Another variable resistor of lead screw actuated type in the prior artemploys a movable member comprising a spring wire having a contactportion for slidably contacting the resistor and a portion for threadingwith a part of the groove of the screw shaft. The variable resistor ofthe type has contained the drawbacks as below. The resistor could nothave a large contact pressure or a large area for the contact portion.This resulted a bad contact and accordingly a complicated procedure forassemblage. Other drawbacks are that pitches and grooves of the screwshaft need particular sizes and configurations; ordinary screw shaftcannot be applied in use; shape of the spring wire is greatlycomplicated and not easy for manufacture; and the backlash is verygreat.

Therefore, it is a general object of the present invention to provide anovel and useful variable resistor of lead screw actuated type which hasovercome and removed the abovedescribed disadvantages.

. Another object of the invention is to provide a variable resistor oflead screw actuated type which is very simple in construction and smallin size. and is accurately operable.

Another object of the invention is to provide a variable resistor oflead screw actuated type in which a movable member can desirably contactthe resistor with appropriate intensive pressure without causing badcontact.

Another object of the invention is to provide a variable resistor oflead screw actuated type in which the movable member can move in goodengagement with the screw without having large backlash or idle rotationof the screw shaft by intense contact pressure.

Another object of the invention is to provide a variable resistor oflead screw actuated type in which the screw shaft can make idlerotations relative to the movable member at a movable end of the shafteven though it erroneously continues its rotation.

Another object of the invention is to provide a variable resistor oflead screw actuated type in which the movable member will not displaceby external shocks but performs accurate slide movements as all times.

Still another object of the invention is to provide a variable resistorof lead screw actuated type which can employ an ordinary screw shaft andwhich is assembled readily and in low manufacturing cost.

These and other objects and features of the invention will becomeapparent from the description set forth hereafter when read inconjunction with the accompanying drawings, in which:

FIG. I is a longitudinal sectional view of one embodiment of thevariable resistor according to this invention;

FIG. 2 is a perspective view of the movable member accommodated in thevariable resistor shown in FIG. 1;

FIG. 3 is partially sectioned perspective viewof a movable memberholder;

FIG. 4 is a bottom view illustrating the meshing engagement of an end ofthe moveable member with a screw shaft;

FIGS. 5A and 5B are respectively views illustrating a relationshipbetween a lead angle of the screw shaft and an inclination angle of anend of meshing engagement portion;

FIG. 6 is a perspective view of the variable resistor according to thisinvention as applied in a noncontact-type tuner;

FIG. 7 is a perspective view of another embodiment of this inventionwith the movable holder removed.

Referring now to FIG. 1, a movable member 10 consists of anelectroconductive leaf spring in a bent form as shown in FIG. 2. A leg11 of the movable member 10 has at its forward end a contact 13 whichslidably contacts a resistor. The movable member 10 extends through abent portion 14 from the leg 11 to a curved protuberance l5 and ameshing portion 16. Between the protuberance l5 and the meshing portion16 there are provided left and right projections I7. The resistor 12 hasa carbon coated resistance or a conductive foil resistance. A movablemember holder 18 holds the movable member I0. The member holder I8 has ahole 20 through which an electroconductive screw shaft I9 is insertedand also has a holding grooves 21 as shown in FIG. 3. The holder 18 ismade of an electric insulating material. An erected portion 22 isprovided at the upper part of the holder 18. An indicator needle 23 isfixed at the upper end of the erected portion 22 (FIG. 6).

The movable member 10 is held in the holding groove 21 of the holder 18and thereafter the screw shaft I9 is inserted through the hole 20 of theholder 18. Thus the slidablc variable resistor is assembled as shown inFIG. 1. In this state, the top portion of the protuberance 15 of themovable member 10 and the tip end of the meshing portion 16 are engagedand meshed with the grooves of the screw shaft 19. The movable member 10is electrically contacted with the screw shaft 19 at these twopositions. Therefore, the movable member I0 and the screw shaft 19 inany case maintain the matual electrical contact nearly completely. Themeshing portion 16, since it contacts with both sidewalls of the grooveof the screw shaft 19, meshes completely with said groove withoutbacklash.

The meshing portion 16 may preferably engage with the groove at aposition distant by eight to 10 pitches from a position where the topportion of the protuberance I5 is engaged with the screw shaft 19. Thus,the distance L between the end of the meshing portion 16 and the tipportion of the protuberance IS'may be expressed by the formulazLg nP,where a pitch of the screw shaft 19 is P, and n is an integer ofapproximately 8 to 10. Accordingly, in case the outer diameter of thescrew is for example 3 mm./ and the pitch P is 0.5 mm., the distance Lmay be 4 to 5 mm. desirably.

Engagement of the tip end of the meshing portion 16 of the movablemember 10 with the screw shaft 19 is now shown in FIG. 4. In case thescrew shaft 19 has a lead angle 0, the meshing portion 16 is inclinedapproximately in an angle from a perpendicular direction to the axis ofthe screw shaft 19 in a reverse direction to the lead angle. Therefore,the direction of the root or crest of thread of the screw shaft 19 andthe inclination of the tip end of the meshing portion 16 constitutes anangle 20. Both corners of the tip end of the meshing portion are roundedin shape. The tip end of the meshing portion 16 is inclined at an angle0 in the reverse direction to the lead angle. Thereby, as laterdescribed, when the movable member is suspended at the end of itsmovement the tip end of the meshing portion 16 will ride and pass overthe screw crest irrespective of the rotating direction of the screwshaft in rotation.

Requirements for the meshing portion in suspension to pass over thecrest of the rotating screw shaft 19 enough smoothly are now explainedwith reference to FIGS. 5A and 58. FIG. 5A shows a vertically sectionedfront elevation of the screw shaft 19. Here, it is assumed that thediameter of a screw crest is d; diameter of a screw root d,; andeffective screw diameter d It is desired that the tip end of the meshingportion 16 will engage the screw approximately in the vicinity of theeffective diameter. Points A and B are now given respectively asintersecting points of the tangent to a point H on the effectivediameter and the diameter of the crest. Thus, the following formula maybe obtained.

HQLX/ 1) If the pitch is provided as P, the values d and d will be givenas d =d-1.082532P and d =d 0.6495 l9P according to the Standard. Theabove formula (2) has been obtained thus in consideration of thepractical values.

From the formula (2 the following will be obtained,

Also, if

I tciie.

rs ew Hence, a line SE is parallel to a line S'D'. Now, the inclinationangle of the line V5 made by a direction vertical to the axis of thescrew shaft may be assumed as Q. Said angle 0 may be a-Ead angle of thescrew. As the line SE is parallel to the line S'I). the line SE also mayhave an angle 0 with respect to the vertical direction of the shaftaxis. Accordingly, if the inclination angle at the end of the meshingportion 16 is B, [#6, provided that its direction is in the reverse.Thus, it is required that the inclination angle [3 at the tip end of themeshing portion 16 is reverse in the direction to the lead angle 0 ofthe screw of the screw shaft 19 and has approximately equal absolutevalue. However, the angle [3 may not strictly be equal to the angle 0but it may substantially be B=01 or thereabout. According to theembodiment, 6 may be between about 2 and 4.

By rotation of the screw shaft 19, the movable member 10 in engagementwith the meshing portion 16 and the protuberance 15 moves to right orleft on FIG. 1 with the holder 18 corresponding to the direction ofrotation of the shaft 19. At the instant, the movable member 10 is ledpositively by the meshing portion 16. Since the curvature of theprotuberance 15 is relatively large compared with the width of the pitchof the screw shaft, the top portion of the protuberance 15 is onlyengaged between adjacent crests of the screw. This causes that themovable member 10 is positively led by the meshing portion 16. Then themeshing portion 16 will not nearly have backlash with respect to thescrew shaft 19. Therefore, the movable member 10 responds directly tothe rotation of the shaft 19 and moves correctly. Then the leg 11 of themovable member 10 is securely contacted to the resistor 12 by its tipportion 13 with its resiliency.

By rotation of the screw shaft 19, the movable member 10 moves to theextreme left of the shaft. In this position, the holder 18 is suspended.The movable member 10 will not move further to left as its engagingportion 14 engages the end of the holder 18. If the operator continuesrotation of the screw shaft 19 by error, the holder 18 and the movablemember 10 are engaged at the left end so that the screw shaft 19 willmake idle rotation. Herein, the forward end of the meshing portion 161sinclined at an angle reverse in direction and approximately equal in theabsolute value with the lead angle of the screw. Therefore the meshingportion 16 will smoothly pass over the crest of the screw shaft 19 andis not probable to prevent the idle rotation of the shaft 19.

The movable member 10 moves toward the right end of the screw shaft 19together with the holder 18 as the shaft 19 rotates and the holder 18 isthere suspended. The movable member 10 will not move further to theright as its projection 17 is engaged in a stepped portion 24 of theholder 18 shown in FIG. 3. If the operator continues rotation of thescrew shaft 19 by error the screw shaft 19 will make idle rotation asthe holder 18 and the movable member 10 are engaged at the right end.The meshing portion 16 will smoothly pass over the crest of the screwshaft 19 in the similar way as described above. There may be provided avertically cut groove for forming a forked shape at the end of the leg11. In this instance, the contact with the resistor will become morestable and a braking force caused from the contact may be lessened.

FIG. 6 shows the variable resistor of the described construction asapplied in the noncontact tuner. By depression of a shaft 30, a facegear 31 engages with a gear 32 fixed at the end of the screw shaft 19and a gear 34. The gear 34 is electrically connected to VHF and UHFtuners (not shown) and provided on a shaft 33 which is rotated byadjustable knob (not shown). By downward movement of the shaft 30, aprojection (not shown) on the shaft 30 will push a brush 35. By thepushing, the brush 35 which is electricallyconnected to the shaft 33will contact the screw shaft 19 and is electrically connected thereto.Terminals 36a and 36b are printed on the circuit base board 37 inconnection to both ends of the resistor 12. The terminals 360 and 36bare applied a predetermined DC voltage.

Now, the shaft 33 is rotated by revolving of an adjusting knob. Therotation of the shaft 33 is transmitted to the screw shaft 19 throughthe gears 34, 31, and 32 resulting in the rotation of the shaft 19. Byrotation of the screw shaft 19, the movable member 10 engaging the screwmoves in the direction corresponding to the rotating direction of theshaft 19 together with the holder 18. By rotation of the screw shaft 19in a definite amount, the portion 13 slidingly contacts the resistor 12and the member 10 moves to a definite position. As a result, a DCvoltage responsive to a desired selected channel is applied on the tunerthrough the shaft 33. The'DC voltage has a voltage value correspondingto the resistance value at the described position.

At the instant, the holder 18 and the erected portion 22 are movedtogether with the movement of the movable member 10. A dial plate 39 onchassis 38 penetrates through the vertical portion 22 of the holder 18.Therefore, the indication of the dial plate 39 by the pointer 23 isperformed in response to the position of the movable member 10.

Preferably, the plate 39 may be used as a mere guide for movement and adial plate may be provided over the pointer 23 so as to make dialindication in cooperation with the pointer 23.

Another embodiment of the variable resistor according to the inventionis now illustrated with reference to FIG. 7. in H0. 7, the movablemember holder is taken away. Throughout FIGS. 1, 2 and 7 like numeralsdenote like parts, and the detailed description thereof is omitted. Amovable member 50 has the meshing portion 16 and the protuberance inengagement with the screw shaft 19 just like the movable member 10 asshown in the preceding embodiment. The movable member 50 has legs 51aand 51b of forked shape at the lower end. Slidable contact portions 52aand 52b at the forward ends of the legs 51a and 51b respectively contactthe two resistors 12a and 12b provided in parallel and separated fromeach other. The legs may be divided into three or more parts.

In one using instance, the resistors respectively have differentresistance values to form different circuits. According to the instance,one movable member will actuate the variable resistor for two circuits.

In another using instance, one resistor 12a, for example, of tworesistors 12a and 12b may be applied a DC voltage as like in theresistor 12 of the above embodiment. The other resistor 12b may consistof a conductor of extremely low resistance value. Then, an output istaken from the resistor 12b instead of from the screw shaft 19. Forobtaining the output from the screw shaft 19 it is required to push abrush against the rotating shaft 19 to thereby obtain an electricalcontact. This would cause the bad contact of the rotating shaft and thebrush. Ac-

cording to the present instance the conductor 12b is usually in a stillstate so that the output can be easily taken out.

Throughout the above-mentioned embodiments the protuberance 15 serves toprevent the unstable movement and to provide a parallel movement withthe screw shaft 19 and the resistor 12. Therefore, if the engagementwith the screw shaft 19 is made only by the meshing portion 16, theprotuberance 15 may have a plane configuration contacting all over thecrests in plurality in place of a curved shape.

The invention may not be confined solely to the abovedescribedembodiments in practice but various modifications can be made in therange of contribance without departing from the spirit and scope of theinvention.

What I claim is:

1. A ,variable resistor comprising a rotatable screw shaft having ascrew on the periphery thereof, a resistor disposed in parallel withsaid screw shaft, a movable member in the form of a bent leaf spring ofelectrically conductive metal, and a movable member holder through whichthe screw shaft passes, said holder holding the movable member, saidmovable member including at one end thereof a slidable contact portioncontacting the resistor, the other end contacting the portions ofgrooves of the screw having an effective screw diameter and aprotuberant middle portion contacting adjacent crests of the screw, theedge line of the other end of said movable member having an inclinationangle with respect to a vertical plane to the axis of said screw shaft,which angle is reversed in direction to the lead angle of the screw andsubstantially equal to the lead angle in absolute value.

2. The variable resistor as claimed in claim 1 wherein said inclinationangle of the edge line of the other end of said movable member issubstantially equal to an angle [3 which is defined as follows:

l where 0 is the absolute value of the lead angle of the screw.

1. A variable resistor comprising a rotatable screw shaft having a screwon the periphery thereof, a resistor disposed in parallel with saidscrew shaft, a movable member in the form of a bent leaf spring ofelectrically conductive metal, and a movable member holder through whichthe screw shaft passes, said holder holding the movable member, saidmovable member including at one end thereof a slidable contact portioncontacting the resistor, the other end contacting the portions ofgrooves of the screw having an effective screw diameter and aprotuberant middle portion contacting adjacent crests of the screw, theedge line of the other end of said movable member having an inclinationangle with respect to a vertical plane to the axis of said screw shaft,which angle is reversed in direction to the lead angle of the screw andsubstantially equal to the lead angle in absolute value.
 2. The variableresistor as claimed in claim 1 wherein said inclination angle of theedge line of the other end of said movable member is substantially equalto an angle Beta which is defined as follows: Beta theta + or - 1* wheretheta is the absolute value of the lead angle of the screw.